1. Field of the Invention
The invention relates generally to wireless telephony, and more specifically to techniques for controlling access to wireless telephone networks.
2. Description of Related Art
At present, there is an ever-increasing demand for personal communications services which will provide reliable voice and data communications, anytime and anywhere, via small, lightweight, portable terminals. The capacity of the existing U.S. cellular telephone network, which uses frequencies in the 824-849 Mhz and 869-894 Mhz bands, may be insufficient to meet this demand. Accordingly, the Federal Communications Commission (FCC) has allocated a portion of the electromagnetic frequency spectrum to PCS (personal communications services). It is possible to utilize existing cellular telephone communications protocols to implement PCS. For example, the service area of a PCS network may be partitioned into a plurality of cells, macrocells, microcells, and/or picocells. A base station, including a processor and a plurality of RF transceivers, manages channel allocation within each cell.
Two important quality-of-service (QOS) criteria for existing cellular networks are the fraction of new calls, and the fraction of handed-off calls, that are blocked due to unavailability of channels. These QOS criteria are also applicable to other types of wireless communications systems, including PCS. A handed-off call refers to a call in progress that is transferred from a first cell site to a second cell site. A channel is any communications channel adapted for carrying information. The definition of a channel depends upon the specific characteristics of a given cellular network. For example, in the case of a conventional frequency-division, multiple-access (FDMA) system, channels consist of an assigned bandwidth in the frequency domain. If one commonly-utilized type of time-division multiple access (TDMA) is employed, channels consist of a given predefined time slot within a conventional FDMA channel. In code-division, multiple-access (CDMA) systems, each channel is uniquely defmed by a predetermined digital code that modulates user information using spread-spectrum modulation techniques. Channels could also be defined in terms of available computing resources at each of the base station processors. However, note that the two quality-of-service criteria set forth above are meaningful, irrespective of the particular type of communications channel employed in a wireless network.
Quality-of-service criteria are used to measure the effectiveness of wireless telephone call admission control policies. These criteria can be employed to formulate three illustrative design objectives: (1) minimizing a linear finction of the new call blocking probability and the handoff call blocking probability, (2) minimizing the new call blocking probability while placing a fixed constraint on the handoff call blocking probability, and (3) minimizing the number of channels while placing fixed constraints on both blocking probabilities (i.e., the blocking of new, as well as handoff, calls). Existing call admission control techniques address the first of the three basic design objectives described above; namely, minimizing a linear function of the new call blocking and handoff call blocking probabilities so long as it is not also desired to simultaneously optimize other design objectives. For example, one such call admission control technique, generally known to those skilled in the art as the guard channel policy, referred to herein as the integral guard channel policity, explicitly reserves a given set of channels for handoff calls. However, existing techniques do not adequately address the two remaining design objectives, which are minimizing the new call blocking probability with a fixed constraint on handoff call blocking, and minimizing the number of channels with fixed constraints on all call blocking probabilities.
Refer to FIG. 1, which sets forth an illustrative prior-art method termed the integral guard channel policy. The method commences at block 101, where the base station processor of a wireless telephone network checks to ascertain whether or not any of the conditions in the immediately following blocks, namely, blocks 103 and 111, occur. At block 103, a test is performed to ascertain whether or not the base station processor is attempting to set up a new call in response to a request that the processor receives from a telephonic device. The negative branch from block 103 leads back to block 101, and the affirmative branch from block 103 leads to block 105. At block 105, the base station processor checks to ascertain whether or not the number of occupied channels is less than a first threshold. If the number of occupied channels is less than a first threshold, the base station processor admits the new call from (or to) the mobile subscriber unit (block 107), and the program loops back to block 101. However, if the number of occupied channels is not less than the first threshold, the base station processor does not admit the new call from (or to) the mobile subscriber unit (block 109), and the program loops back to block 101.
At block 111, the processor checks to see whether or not the base station processor is attempting to set up a call that is being handed off. If not, the program loops back to block 101. If so, the program continues to block 113, where the base station processor checks to ascertain whether or not there are any unoccupied channels. If there are any unoccupied channels, the base station processor admits the handoff call from the mobile subscriber unit attempting a handoff (block 115), and the program loops back to block 101. However, if there are not any unoccupied channels, the base station processor does not admit the handoff call from the mobile subscriber unit attempting a handoff (block 117), and the program loops back to block 101.